Swallow populations across the decades

Swallow boxes on Kent Island. Photo by John Lichter.

New paper lead by graduate student Tara Imlay from the University of Dalhousie in Nova Scotia (and including Professor Nat Wheelwright from Bowdoin and Professor Marty Leonard from Dalhousie) is out in Ecosphere. Imlay and her colleagues are searching for explanations for the dramatic declines that occurred in many swallow populations in the 1980's. They therefore examined breeding success and whether it was related to phenology or climate change for bank, barn, cliff, and tree swallows in datasets (including Kent Island!) that spanned 57 years. Surprisingly, given the declines in swallows, only bank swallows showed consistent declines in breeding success over the decades. In addition Bank swallows were the only species that did not advance their egg laying timing earlier across decades, all other species are laying eggs 8-10 days earlier than they were in the 1960's. This research indicates that for three of these four swallows, population declines do not seem to be driven by declines in breeding success. This highlights the need to examine factors that may be causing bird mortalities during migration or over the winter season. We only had one breeding pair of tree swallows on Kent Island last summer, but the boxes are up and will continued to be monitored.